When formed into such articles as molded objects or films, synthetic polymers are known to generate and accumulate electrostatic charges. When charged, such objects tend to accumulate concentrations of dirt and soil which are unsightly in appearance and interfere with the use of such objects. When nylon or polyester polymers are formed into fibers, the electrostatic charges create processing problems whereas in consumer use, carpeting made from such synthetic fibers has a tendency to generate annoying shocks in cold, dry weather, while in apparel, the charged fabric clings embarassingly to the wearer and shocks the wearer when the garment is being removed. Furthermore, such garments have an increased tendency to attract lint and soil.
The problem of electrostatic charge and arcing that it can create, is also of great concern in clean rooms, such as hospital surgery rooms, as well as chemical plants and laboratories, and electronic equipment, in particular. Arcing due to an electrostatic charge can cause an explosion or can damage electronic equipment.
To overcome the static electricity problem, topical antistats have been used to eliminate the electrical charges, however, such treatments have proven to be of little benefit in the consumer applications due to lack of permanency. Other methods used to reduce the electrostatic charges included copolymerization of monomers containing ionizable groups, surface grafted polymerization of antistatic monomers, inclusion of metallic fibers or carbon-coated filaments, incorporation of an antistatic additive in the matrix polymer, and the like.
The prior art is replete with teachings to reduce antistatic charges in various polymeric structures. Certain prior art patents describe the incorporation of antistatic materials in various polymeric structures which are used to mold or extrude rigid objects such as luggage, protective covers, and automobile parts. There is also a vast body of prior art patent literature directed to the elimination of the static charges in fiber and films.
This invention is directed to plastic materials, which include thermoplastic compositions and thermosets, containing an effective amount of an epihalohydrin-containing polymer as an antistatic agent. Examples of thermoplastic materials include polymers of acrylonitrile, butadiene, and styrene, also known as ABS polymers; polyamides or nylons; polyesters; polyvinyl chloride; chlorinated polyvinyl chloride; and polycarbonates. Examples of thermosetting materials include epoxy and phenolic resins. The plastic materials contain 1 to 50 weight parts of an epihalohydrin polymer antistatic agent per 100 weight parts of the plastic material.
The deleterious effects of electrostatic charge is reduced or eliminated by inclusion in a plastic material an epihalohydrin antistatic agent selected from epihalohydrin homopolymers and epihalohydrin copolymers. An effective amount of the antistatic agent is used in the plastic material to induce charge dissipation by at least 50% in less than 10 seconds on application of 1000 volts of direct current at 23.5xc2x0 C. and 50% Relative humidity. More specifically, the antistatic agent can be used in amount of 1 to 50 weight parts, preferably 2 to 30 weight parts, per 100 weight parts of the plastic material. Therefore the plastic material comprises between 67 and 99 weight percent of the composition and the antistatic agent comprises between 1 and 33 weight percent of the composition.
The antistatic agent can be in liquid or solid form. When in liquid form, it can be blended with the solid plastic material by mixing the two materials together until the plastic material absorbs the liquid antistatic agent. When the antistatic agent is in a solid form, such as powder, it is mixed with the plastic material until it is uniformly distributed throughout the plastic material. It should be apparent that the antistatic agent becomes an integral part of the plastic material after it is molded, however, it can also be used as a surface treatment therefor.
The Dreyfuss U.S. Pat. No. 3,850,856 and 3,850,857 disclose commercially available liquid epihalohydrin polymers prepared by cationic ring-opening polymerization. The epihalohydrin polymers disclosed in these patents can be used as antistatic agents in the manner described herein. The ""857 Dreyfus patent discloses a process for polymerizing an epihalohydrin using as a catalyst a trialkyloxonium salt of an HMF6 acid where M is a Group V element selected from phosphorous, arsenic, and antimony. The ""856 Dreyfuss patent discloses an improvement over the ""857 patent wherein polymerization of an epihalohydrin is carried out in the presence of water or ethylene glycol. The resulting polymers of an epihalohydrin prepared pursuant to the Dreyfuss patent ""856 have hydroxyl termination. Any of the other alkylene glycols can also provide hydroxyl termination.
The liquid antistatic agents referred to herein have Brookfield viscosity below 16,000,000 cps at 25xc2x0 C. More specifically, such liquid polymers or antistatic agents have viscosity measured at 25xc2x0 C. in the range of 100 to 10,000,000 cps, preferably 200 to 2,000,000 cps and have number average molecular weight of 200 to 30,000, preferably 300 to 15,000, as determined by gel permeation chromatography using polystyrene as the calibration standard.
Solid epihalohydrin polymers are also well known commercial elastomers which can also be used as antistatic agents. A particularly useful class of these materials are copolymers of an epihalohydrin and an alkylene oxide. These copolymers are readily prepared by polymerization in mass or solution with catalysts normally formed by reacting an organoaluminum compound with water, and optionally, with a small amount of a chelating agent. These copolymers normally have a number average molecular weight greater than about 30,000, preferably in excess of 60,000, as determined by gel permeation chromatography. The Oetzel U.S. Pat. No. 4,251,648 describes such solid polymers of epihalohydrin also containing an unsaturated epoxy comonomer which makes it possible to cure such copolymers with an organic peroxide.
The epihalohydrin monomers useful in preparing polymeric epihalohydrin antistatic agents of this invention include epichlorohydrin, epibromohydrin, epiiodohydrin, and epifluorohydrin, although eipchlorohydrin is preferred. The antistatic agents include the epihalohydrin homopolymers and copolymers thereof with one or more comonomers selected from 1,2-epoxide monomers, particularly alkyl glycidyl ethers and oxirane-containing monomers or alkylene oxides of 2 to 6 carbon atoms, particularly ethylene oxide and propylene oxide and mixtures thereof. In these copolymers, amount of an epihalohydrin can vary from about 5 to 95 weight parts whereas one or more of the comonomers are used in an amount of 95 to 5 weight parts. Particularly preferred copolymers are solid, as in powder form, consisting of 5 to 95 weight parts epihalohydrin, preferably 10 to 60 weight parts, with 95 to 5 weight parts, preferably 90 to 40 weight parts, of one or more comonomers, such as ethylene oxide or propylene oxide, all on the basis of a total of 100 weight parts. Based upon these weight percentages, the ratio by weight of the epihalohydrin to the oxirane-containing monomer is from about 1:19 to about 1:1. The presence of an epihalohydrin in the antistatic agent appears to improve compatibility between the antistatic agent and the plastic material with which it is blended.
Other antistatic agents can also be included in the plastic compositions, along with the antistatic agents already described. Some examples of such other antistatic agents include long chain and ethoxylated amines and amides, and quarternary ammonium salts.
The plastic materials are generally divided into thermoplastics and thermosets. This invention is generally directed to imparting antistatic character to plastic materials, including engineered plastics. Thermosetting resins are those in which a heat-stable crosslinked polymer network extends throughout the finished fabricated article. This is in contrast to thermoplastics, which can be made to soften and flow by the application of heat.
As already noted, the plastic materials can be modified with an antistatic agent in order to impart antistatic character thereto. Whether the antistatic agent is liquid or in solid form, the object of the invention herein is attained by mixing the antistatic agent with a suitable plastic material until the materials are uniformly dispersed. Examples of suitable thermoplastic materials include ABS polymers, polyvinyl chloride, chlorinated polyvinyl chloride, nylons and polyamides, polycarbonates, and polyesters. Examples of thermosetting materials include epoxies and phenolics.
Acrylonitrile-butadiene-styrene (ABS) copolymers have a wide variety of compositions, preparation conditions, and properties. The copolymers are typically tough and rigid, easy to extrude or mold, and have good abrasion resistance. ABS copolymers have a rubber substrate and a rigid phase. Generally, the rigid phase includes acrylonitrides and vinyl aromatic compounds. The vinyl aromatic compounds can include components such as styrene. The ABS copolymer is composed of up to about 60 weight percent of the rubber substrate and at least 40 weight percent of the acrylonitride and vinyl aromatic. They can be blended with other polymers, especially with poly(vinyl chloride), and can be shaped by almost any plastics-fabrication process: injection molding, extrusion, or thermoforming. They are used in many automotive, marine and communication applications. In building products, they are used for pipes, ducts, and structural foam.
Proportions of monomers normally used to make ABS copolymers are about 40 to 90% of combined acrylonitrile and styrene, with about 60 to 10 parts of butadiene. Butadiene is the rubber substrate of the ABS copolymer. The amount of acrylonitrile is preferably from about 10 to 60% by weight. Blends of ABS copolymers with other polymers such as vinyl chloride polymers, styrene polymers, methyl methacrylate polymers, polyurethanes, polycarbonates, and the like may also be used. Any ABS copolymer that can be extruded or molded can be used in accordance with this invention.
Vinyl chloride polymers are produced in two main types, homopolymers and copolymers, usually with vinyl acetate or one or more other polymerizable olefinic monomers having at least one terminal CH2xe2x95x90C less than group. Both types can be plasticized by a wide variety of plasticizers, usually esters. Rigid or unplasticized PVC is used extensively for pipe. The plasticized material is used largely in floor coverings. The homopolymer itself is inherently fire resistant, but addition of plasticizers, unless they are especially fire resistant, considerably reduces this characteristic.
Rigid polyvinyl chloride is a low cost thermoplastic material having in combination, good impact strength, good moldability, low weight, and resistance to combustion, corrosion and attack by acids. For these reasons, it has found wide application in products such as building panels, pipes, pipe fittings, ducts, blown bottles and the like, which are made from rigid vinyl polymer compounds by extrusion, calendering or molding. To make polyvinyl chloride suitable for fabrication by these methods, it is necessary to add to it one or more stabilizers, lubricants, pigments and polymer modifiers.
The chlorinated polyvinyl chloride employed in the present invention can be readily prepared by the post-chlorination of commercially available polyvinyl chloride. Prior to post-chlorination, the polyvinyl chloride generally has a chlorine content of about 56.7% by weight, a glass transition temperature of from about 75xc2x0 to 80xc2x0 C., and a density of about 1.40 grams per cubic centimeter. Polyvinyl chloride can be post-chlorinated by a number of procedures including chlorination in a solution; chlorination in an aqueous suspension, or a suspension in a swelling agent; and direct chlorination of dry, polyvinyl chloride powder.
Chlorinated polyvinyl chloride is generally defined as having a minimum chlorine content of at least 60% by weight, and for practical purposes, a maximum chlorine content of about 75%. In a preferred embodiment, chlorinated polyvinyl chloride has a chlorine content of about 64 to 73%.
The glass transition temperature (Tg) is that temperature below which a polymer remains hard and glassy as opposed to soft and rubbery. The glass transition temperature of chlorinated polyvinyl chloride increases with increasing chlorine content. Polyvinyl chloride itself has a glass transition temperature of about 75xc2x0-80xc2x0 C., while typical glass transition temperatures for chlorinated polyvinyl chloride suitable for the present invention are about 87xc2x0 C. for 60% chlorine content, about 106xc2x0 C. for 64% chlorine content, about 128xc2x0 C. for 68% chlorine content, and about 178xc2x0 C. for 75% chlorine content.
Chlorinated polyvinyl chloride can be a homopolymer or a copolymer thereof with a minor amount of one or more copolymerizable monomers. Generally, up to about 20% by weight of the vinyl chloride can be replaced by one or more of copolymerizable monomers, such as monoolefinic copolymerizable monomers.
Nylon is a generic name for any long-chain, synthetic, polymeric amides in which recurring amide groups are integral with the main polymer chain. There is a wide choice of starting materials from which polyamides can be synthesized. The two primary mechanisms for polyamide manufacture are condensation of a diamine and a dibasic acid, or their equivalents, or polymerization of cyclic monomers.
Polycarbonates are a special class of polyesters derived from the reaction of carbonic acid derivatives with aromatic, aliphatic, or mixed diols. They can be produced by reacting phosgene with a diol in the presence of an appropriate hydrogen chloride acceptor, or by melt transesterification reaction of a diol and a carbonate ester. The three dihydrobenzenes, i.e., hydroquinone, resorcinol, and catechol, can react with phosgene in pyridine. Hydroquinone and resorcinol yield polymers whereas catechol produces a cyclic carbonate. Diethylene glycol chloroformate can be reacted with allyl alcohol to yield a polycarbonate that is highly crosslinked, colorless, scratch-resistant and transparent which is used in optical applications. Aromatic polycarbonates are highly stable to heat, are mechanically tough, transparent engineering thermoplastics.
Polycarbonates are frequently employed as lightweight, break-resistant glass substitutes in light-transmission applications. An example of such an application is transparent canopies for high-speed aircraft. The high impact strength combined with transparency and high flexural strength, make polycarbonate sheet a candidate for bullet-resistant glazing.
Thermoplastic polyesters are condensation products that are characterized by many ester linkages distributed along the polymer backbone. The first of this class to be commercialized was poly(ethylene terephthalate). It was introduced in 1953 as a textile fiber and soon thereafter in film form. In 1966, the first injection-molding grades of poly(ethylene terephthalate) were introduced, but recent injection-molding grades of modified poly(ethylene terephthalate) show improvements over the earlier materials. Poly(butylene terephthalate), also is referred to as poly(tetramethylene terephthalate), was first introduced commercially in 1970. Early injection-molding grades included nonreinforced, glass-reinforced, and flame-retardant products. It is characterized by excellent mold flow and short molding cycles with excellent chemical resistance and performance at elevated temperature.
Thermoset polyesters are macromolecules with polyester backbones derived from the interaction of unsaturated acids or anhydrides and polyhydric alcohols. The reaction normally proceeds at 190-220xc2x0 C. until a predetermined acid value-viscosity relationship has been achieved. Solutions of these polymers in vinyl monomers, such as styrene, often are called polyester resins. They are compounded with fillers or fibers, or both, in the liquid stage and then are cured with the aid of free-radical initiators to yield thermoset articles. Market penetration, especially in the area of fiber-glass reinforcement, is greatly enhanced as a result of greater latitudes in compounding and processing than is possible with other polymeric systems. Thermoset polyesters can be mass-cast, laminated, molded, pultruded, and made into gel coats in a variety of colors. Depending on the application, the physical and chemical properties of the product often can be met by judicious choice of polyester backbone ingredients and the type and amount of the diluent vinyl monomer.
The epoxy resins are thermosetting polyethers which can be made by condensing an epihalohydrin, particularly epichlorohydrin, with a polyhydric phenol in the presence of an alkali. The phenol can be diphenylolpropane or bisphenol A. An excess of an epihalohydrin is used to insure the presence of epoxide groups on the ends of the polymer chains.
The epoxy resins have limited application in the uncured state. Curing reactions involve the hydroxyl groups along the chain and the epoxy end groups. Curing agents include thermosetting resins with methylol groups present, fatty acids or acid anhydrides, and amines or other nitrogen compounds. Amines are the preferred curing agents. The cured resins have good flexibility, adhesion, and chemical resistance.
The chief commercial use of the epoxide resins is in surface coatings. They can be combined with phenolic resins for use in the internal coating of food cans or in ware enamels, or with urea resins to give white enamels. Other uses of the epoxy resins include casting or potting resins for embedding electrical components, low pressure laminates, usually with glass fibers, adhesives, and stabilizers for vinyl resins.
Phenolic thermosetting resins have been known for a long time. Phenols react with aldehydes to give condensation products if there are free positions on the benzene ring ortho and para to the hydroxyl group. Formaldehyde is by far the most reactive aldehyde and is used almost exclusively in commercial production. The reaction is always catalyzed either by acids or bases. The nature of the product is greatly dependent on the type of catalysts used. Urea-formaldehyde and melamine-formaldehyde resins are also included in this category.
The first products of the alkali-catalyzed reaction between a phenol and formaldehyde are known as resoles. If all three of the ortho and para positions in the phenol are free to react, crosslinked materials are quickly formed. The reactions are normally separated into three known phases of A-stage, B-stage, and C-stage. In the final stage of reaction or the C-stage, a great deal of crosslinking takes place and the resin becomes insoluble and infusible.
Phenolic resins are widely used as adhesives, for low pressure laminating, in varnishes, and in coatings.
Many of plastic materials described above are commercial and are readily available. They can be modified by incorporating therein an effective amount of an antistatic agent in order to impart thereto antistatic character, as well as other conventional additives. Such modified plastic materials can then be used to make a great variety of articles such as carpeting, luggage, protective covers, automobile parts, and the like.
In preparing samples for testing in examples that follow, a Brabender mixer with a cam head was used. The maximum temperature used for the various plastic materials was as follows:
ABSxe2x80x94180xc2x0 C.
PVCxe2x80x94160xc2x0 C.
CPVCxe2x80x94180xc2x0 C.
SAN(copyright)xe2x80x94180xc2x0 C